II] PRELIMINARY NOTE 43 



must not be omitted, for, apart from the peculiar charm of style which 

 marks it, it contains some singularly helpful bibliographical data. But 

 the study of the original sources, so far as that is possible, is a duty 

 which cannot be avoided, and in what follows I have been careful 

 to copy down no statement from a previous review when it was 

 possible to read the actual words of the writer himself. 



This practice of going to the originals is made peculiarly necessary 

 in a case such as the present one, when the history of a subject is 

 to be regarded from an entirely new angle. My intention is to give 

 here the sketch of a history of embryology consistently from the 

 physico-chemical angle, and to show, at one and the same time, how 

 our knowledge of the development of the embryo has come into being, 

 and how throughout the process what we now call the physico- 

 chemical foundations of embryonic growth have from time to time 

 received attention, even though it was largely speculative. Since few 

 have previously examined the history of the subject, and none from 

 this angle, I have in many cases come upon interesting facts which 

 have remained unknown owing to the very attitude of mind pre- 

 viously adopted. 



Finally, I would defend the arrangement of my Sections only on 

 the ground that it is suitable in the present state of historical know- 

 ledge. I say little about embryology in ancient China and ancient 

 India, because on the basis of what we know there is little to say, 

 not because it was intrinsically less interesting than the embryology 

 of Mediterranean antiquity and the later West, though this may turn 

 out to be the case. I do not propose a framework for historical facts 

 in what follows ; I only attempt to bring them together, and to reveal 

 some of the relationships between them. If the traditional frame- 

 work turns out to be badly constructed — and there are many signs 

 that it may — the facts can be rearranged. 



The history of single forms of scientific knowledge is in a way 

 happier because containing more of continuity than that of civilisa- 

 tion as a whole. The assiduity with which men of different periods 

 in the rise and decHne of a culture pursue the different forms of 

 human experience may, as Spengler has shown, vary much, but those 

 forms remain fundamentally the same, even if their manifestations 

 are profoundly changed. That science, at any rate, does maintain 

 some sort of continuity whatever gaps there may be between the 

 phases of its progress, is a belief agreeable with all the available facts, 

 and one which no criticism will easily shake. 



